Date: 6/22/25 10:00 pm From: Matt Baumann <000016aa48a8d92d-dmarc-request...> Subject: Re: [BIRDWG01] Colorado Booby ID
Hi all,
Fwiw, thought I would pass along our study where we sequenced both the New Mexico and the previous Colorado brown booby specimens. Both birds unequivocally originated from the Caribbean.
As far as we could tell, inland cocos/brown boobies east of AZ/NV have all been identified or presumed to be browns. That pattern can certainly change but plumage overlap between the species muddies the water.
> On Jun 22, 2025, at 10:43 PM, Matt Baumann <mbaumann22...> wrote:
>
> Hi all,
>
> Fwiw, thought I would pass along our study where we sequenced both the New Mexico and the previous Colorado brown booby specimens. Both birds unequivocally originated from the Caribbean.
>
> As far as we could tell, inland cocos/brown boobies east of AZ/NV have all been identified or presumed to be browns. That pattern can certainly change but plumage overlap between the species muddies the water.
>
> Salvage those inland seabirds when possible.
>
> https://www.researchgate.net/publication/377866630_Freshwater_parasites_as_potential_barriers_to_seabird_dispersal_Evidence_from_vagrant_booby_specimens_in_western_North_America >
> Matt Baumann
> Albuquerque, NM
>
>
> Sent from my iPhone
>>> On Jun 20, 2025, at 9:23 AM, Peter Pyle <ppyle...> wrote:
>>>
>> Great discussion and I'm pleased to be enlightened about the distribution of nominate (Atlantic) Brown Boobies in inland North America. Eric and I have been working a lot on the separation of Cocos (brewsteri) from Pacific (plotus) BRBO, and at least I am not as familiar with the separation of nominate from brewsteri. Thus our leanings to Cocos Booby for the Colorado bird should probably be straightened up a bit per David's comments.
>>
>> There is a specimen of plotus from Alaska but otherwise no confirmed records off our coast north of Mexico (where Eric has identified 1-2 plotus from photographs taken near islands far off Baja). The two best candidates are an adult female from the Farallones in 1992, prior to the incursion of brewsteri up our coast, and a more recent record of one on a boat in the Gulf of Alaska but neither can be confirmed.
>>
>> To answer Paul's question, I believe most Cocos Boobies dispersing north of the breeding grounds are young birds, followed by adult females, with adult males least frequent. This is a common pattern we see in irruptive species, the adult males apparently displacing the others when food becomes scarcer. During the 2013-2014 invasion of 100s of Blue-footed Boobies up the West Coast, 95% of these were first cycle birds. Male brewsteri begin to get paler heads in the second cycle but don't get the fully white-headed look until 3-4 years of age or later, and these older males could be the last to disperse from breeding areas. That said, we have had some fully white headed males as far north as the Farallones. One in an aerial photograph was initially identified as a juvenile Magnificent Frigatebird.
>>
>> Sea surface temps off the West coast have been very cold over the last few years. Once we get an ENSO event or the like, I bet the numbers of Cocos Boobies will increase again.
>>
>> Best to all, Peter
>>
>>
>>> On 6/20/2025 4:50 AM, Paul Lehman wrote:
>>> Ah, the long-standing question about why are there so few clear adult male looking Cocos Boobies with obvious pale heads seen along the U.S. West Coast. We've been talking about that for a couple years now. Even here in Southern California, where there are a couple Island colonies of boobies, and where at least up till the last year or so we would see multiple birds per pelagic trip, we would see extremely few clear adult males with pale heads. Here in San Diego County waters, for example, for many years we would typically see between 3 and 8 boobies per trip and we might do almost 10 trips per year, and on average I would see only one or maybe two pale-headed adult males per year. Pretty much everyone else has the same experience In this region. We wondered if perhaps only the oldest adult males get pale heads, and so everything else have dark heads like females, but we really have no idea why this ratio of clear pale-headed male birds is so low...... I would also add that there's been a noticeable decline in numbers in the past 2 years locally.
>>> Paul Lehman, San Diego
>>>
>>> Sent from AOL on Android
>>> On Thu, Jun 19, 2025 at 6:33 PM, Wayne Hoffman<whoffman...> wrote: Hi -
>>>
>>> Your mention that both this bird and the previous Colorado bird were females reminded me that when "Brown" Boobies (later split as Cocos Boobies) became regular in small numbers on the Oregon coast a decade or so ago, both adults and subadults were occurring, but no birds identifiable as adult male Cocos Boobies had been documented, at least as of 2018 when I left Oregon. So I wonder if female "Brown" Boobies are more likely to wander than males? Similar sex biases in vagrancy are documented in other birds (e.g. Ancient Murrelets).
>>>
>>> Wayne Hoffman
>>>
>>>
>>> ----- Original Message -----
>>> From: "David Sibley" <sibleyguides...>
>>> To: "BIRDWG01" <BIRDWG01...>
>>> Sent: Thursday, June 19, 2025 5:17:22 PM
>>> Subject: Re: [BIRDWG01] Colorado Booby ID
>>>
>>> Following up on this after more photo study. I still think this bird is a better match for Atlantic Brown Booby, but can't rule out Cocos with certainty.
>>>
>>> For comparison, this subadult Brown from Maryland is an almost exact match - https://macaulaylibrary.org/asset/624857879 >>> This Cocos from Costa Rica is also very close - https://macaulaylibrary.org/asset/629034516 >>>
>>> Bill color, bill shape, and eye color seem to be no help in ID.
>>>
>>> One thing that does seem fairly consistent in photos I've looked at is that Cocos has a wider ring of bare skin behind the eye, and by that feature the Colorado bird matches Brown.
>>>
>>> And the bare skin on the chin of Cocos seems to average a little drabber and greener, Brown Booby more yellow, again the CO bird matches Brown.
>>>
>>> Those are pretty much the only differences I can see for a subadult female like this, and for now I would not feel confident identifying either species out of range based on those things. But maybe one could argue that Colorado is within the "expected" range for Brown Booby?
>>>
>>> Colorado's prior record looks like an adult female Atlantic Brown Booby. Cocos adult female typically has a greener face and darker brownish bill (but there is overlap).
>>>
>>> Best,
>>> David
>>>
>>> <sibleyguides...>
>>> www.sibleyguides.com
>>>
>>>
>>>
>>>>> On Jun 18, 2025, at 11:57 AM, Rachel Hopper <hopkohome8...> wrote:
>>>>
>>>> Colorado just had its second record of a booby, found on June 16th & seen early again on the 17th after which it disappeared.
>>>>
>>>> It was found in a tree out on the prairie in far SE CO. No water body even close.
>>>>
>>>> There are several photos of the bird, which did take flight a few times, always coming back to land in an Elm tree. At one point it was on the ground.
>>>>
>>>> We are trying to determine if this is a Brown Booby or Cocos Booby. Possibly not a full adult. Any help would be appreciated.
>>>>
>>>> You can view the photos of the bird here on these 3 checklists:
>>>>
>>>> https://ebird.org/checklist/S251486607 >>>>
>>>> https://ebird.org/checklist/S251577330 >>>>
>>>> https://ebird.org/checklist/S251215877 >>>>
>>>> -----------------------
>>>> Rachel Kolokoff Hopper
>>>> Ft. Collins, CO
>>>>
>>>>
>>>> Archives: https://listserv.ksu.edu/birdwg01.html >>>
>>> Archives: https://listserv.ksu.edu/birdwg01.html >>>
>>> Archives: https://listserv.ksu.edu/birdwg01.html >>>
>>> Archives: https://listserv.ksu.edu/birdwg01.html >>
>>
>> Archives: https://listserv.ksu.edu/birdwg01.html
Date: 6/20/25 8:24 am From: Peter Pyle <ppyle...> Subject: Re: [BIRDWG01] Colorado Booby ID
Great discussion and I'm pleased to be enlightened about the
distribution of nominate (Atlantic) Brown Boobies in inland North
America. Eric and I have been working a lot on the separation of Cocos
(brewsteri) from Pacific (plotus) BRBO, and at least I am not as
familiar with the separation of nominate from brewsteri. Thus our
leanings to Cocos Booby for the Colorado bird should probably be
straightened up a bit per David's comments.
There is a specimen of plotus from Alaska but otherwise no confirmed
records off our coast north of Mexico (where Eric has identified 1-2
plotus from photographs taken near islands far off Baja). The two best
candidates are an adult female from the Farallones in 1992, prior to the
incursion of brewsteri up our coast, and a more recent record of one on
a boat in the Gulf of Alaska but neither can be confirmed.
To answer Paul's question, I believe most Cocos Boobies dispersing north
of the breeding grounds are young birds, followed by adult females, with
adult males least frequent. This is a common pattern we see in irruptive
species, the adult males apparently displacing the others when food
becomes scarcer. During the 2013-2014 invasion of 100s of Blue-footed
Boobies up the West Coast, 95% of these were first cycle birds. Male
brewsteri begin to get paler heads in the second cycle but don't get the
fully white-headed look until 3-4 years of age or later, and these older
males could be the last to disperse from breeding areas. That said, we
have had some fully white headed males as far north as the Farallones.
One in an aerial photograph was initially identified as a juvenile
Magnificent Frigatebird.
Sea surface temps off the West coast have been very cold over the last
few years. Once we get an ENSO event or the like, I bet the numbers of
Cocos Boobies will increase again.
Best to all, Peter
On 6/20/2025 4:50 AM, Paul Lehman wrote:
> Ah, the long-standing question about why are there so few clear adult male looking Cocos Boobies with obvious pale heads seen along the U.S. West Coast. We've been talking about that for a couple years now. Even here in Southern California, where there are a couple Island colonies of boobies, and where at least up till the last year or so we would see multiple birds per pelagic trip, we would see extremely few clear adult males with pale heads. Here in San Diego County waters, for example, for many years we would typically see between 3 and 8 boobies per trip and we might do almost 10 trips per year, and on average I would see only one or maybe two pale-headed adult males per year. Pretty much everyone else has the same experience In this region. We wondered if perhaps only the oldest adult males get pale heads, and so everything else have dark heads like females, but we really have no idea why this ratio of clear pale-headed male birds is so low...... I would also add that there's been a noticeable decline in numbers in the past 2 years locally.
> Paul Lehman, San Diego
>
> Sent from AOL on Android
>
> On Thu, Jun 19, 2025 at 6:33 PM, Wayne Hoffman<whoffman...> wrote: Hi -
>
> Your mention that both this bird and the previous Colorado bird were females reminded me that when "Brown" Boobies (later split as Cocos Boobies) became regular in small numbers on the Oregon coast a decade or so ago, both adults and subadults were occurring, but no birds identifiable as adult male Cocos Boobies had been documented, at least as of 2018 when I left Oregon. So I wonder if female "Brown" Boobies are more likely to wander than males? Similar sex biases in vagrancy are documented in other birds (e.g. Ancient Murrelets).
>
> Wayne Hoffman
>
>
> ----- Original Message -----
> From: "David Sibley" <sibleyguides...>
> To: "BIRDWG01" <BIRDWG01...>
> Sent: Thursday, June 19, 2025 5:17:22 PM
> Subject: Re: [BIRDWG01] Colorado Booby ID
>
> Following up on this after more photo study. I still think this bird is a better match for Atlantic Brown Booby, but can't rule out Cocos with certainty.
>
> For comparison, this subadult Brown from Maryland is an almost exact match - https://macaulaylibrary.org/asset/624857879 > This Cocos from Costa Rica is also very close - https://macaulaylibrary.org/asset/629034516 >
> Bill color, bill shape, and eye color seem to be no help in ID.
>
> One thing that does seem fairly consistent in photos I've looked at is that Cocos has a wider ring of bare skin behind the eye, and by that feature the Colorado bird matches Brown.
>
> And the bare skin on the chin of Cocos seems to average a little drabber and greener, Brown Booby more yellow, again the CO bird matches Brown.
>
> Those are pretty much the only differences I can see for a subadult female like this, and for now I would not feel confident identifying either species out of range based on those things. But maybe one could argue that Colorado is within the "expected" range for Brown Booby?
>
> Colorado's prior record looks like an adult female Atlantic Brown Booby. Cocos adult female typically has a greener face and darker brownish bill (but there is overlap).
>
> Best,
> David
>
> <sibleyguides...>
> www.sibleyguides.com
>
>
>
>> On Jun 18, 2025, at 11:57 AM, Rachel Hopper <hopkohome8...> wrote:
>>
>> Colorado just had its second record of a booby, found on June 16th & seen early again on the 17th after which it disappeared.
>>
>> It was found in a tree out on the prairie in far SE CO. No water body even close.
>>
>> There are several photos of the bird, which did take flight a few times, always coming back to land in an Elm tree. At one point it was on the ground.
>>
>> We are trying to determine if this is a Brown Booby or Cocos Booby. Possibly not a full adult. Any help would be appreciated.
>>
>> You can view the photos of the bird here on these 3 checklists:
>>
>> https://ebird.org/checklist/S251486607 >>
>> https://ebird.org/checklist/S251577330 >>
>> https://ebird.org/checklist/S251215877 >>
>> -----------------------
>> Rachel Kolokoff Hopper
>> Ft. Collins, CO
>>
>>
>> Archives: https://listserv.ksu.edu/birdwg01.html >
> Archives: https://listserv.ksu.edu/birdwg01.html >
> Archives: https://listserv.ksu.edu/birdwg01.html >
>
> Archives: https://listserv.ksu.edu/birdwg01.html
Date: 6/20/25 4:51 am From: Paul Lehman <00000ae015dd4920-dmarc-request...> Subject: Re: [BIRDWG01] Colorado Booby ID
Ah, the long-standing question about why are there so few clear adult male looking Cocos Boobies with obvious pale heads seen along the U.S. West Coast. We've been talking about that for a couple years now. Even here in Southern California, where there are a couple Island colonies of boobies, and where at least up till the last year or so we would see multiple birds per pelagic trip, we would see extremely few clear adult males with pale heads. Here in San Diego County waters, for example, for many years we would typically see between 3 and 8 boobies per trip and we might do almost 10 trips per year, and on average I would see only one or maybe two pale-headed adult males per year. Pretty much everyone else has the same experience In this region. We wondered if perhaps only the oldest adult males get pale heads, and so everything else have dark heads like females, but we really have no idea why this ratio of clear pale-headed male birds is so low...... I would also add that there's been a noticeable decline in numbers in the past 2 years locally.
Paul Lehman, San Diego
Sent from AOL on Android
On Thu, Jun 19, 2025 at 6:33 PM, Wayne Hoffman<whoffman...> wrote: Hi -
Your mention that both this bird and the previous Colorado bird were females reminded me that when "Brown" Boobies (later split as Cocos Boobies) became regular in small numbers on the Oregon coast a decade or so ago, both adults and subadults were occurring, but no birds identifiable as adult male Cocos Boobies had been documented, at least as of 2018 when I left Oregon. So I wonder if female "Brown" Boobies are more likely to wander than males? Similar sex biases in vagrancy are documented in other birds (e.g. Ancient Murrelets).
Wayne Hoffman
----- Original Message -----
From: "David Sibley" <sibleyguides...>
To: "BIRDWG01" <BIRDWG01...>
Sent: Thursday, June 19, 2025 5:17:22 PM
Subject: Re: [BIRDWG01] Colorado Booby ID
Following up on this after more photo study. I still think this bird is a better match for Atlantic Brown Booby, but can't rule out Cocos with certainty.
Bill color, bill shape, and eye color seem to be no help in ID.
One thing that does seem fairly consistent in photos I've looked at is that Cocos has a wider ring of bare skin behind the eye, and by that feature the Colorado bird matches Brown.
And the bare skin on the chin of Cocos seems to average a little drabber and greener, Brown Booby more yellow, again the CO bird matches Brown.
Those are pretty much the only differences I can see for a subadult female like this, and for now I would not feel confident identifying either species out of range based on those things. But maybe one could argue that Colorado is within the "expected" range for Brown Booby?
Colorado's prior record looks like an adult female Atlantic Brown Booby. Cocos adult female typically has a greener face and darker brownish bill (but there is overlap).
Best,
David
<sibleyguides...>
www.sibleyguides.com
> On Jun 18, 2025, at 11:57 AM, Rachel Hopper <hopkohome8...> wrote:
>
> Colorado just had its second record of a booby, found on June 16th & seen early again on the 17th after which it disappeared.
>
> It was found in a tree out on the prairie in far SE CO. No water body even close.
>
> There are several photos of the bird, which did take flight a few times, always coming back to land in an Elm tree. At one point it was on the ground.
>
> We are trying to determine if this is a Brown Booby or Cocos Booby. Possibly not a full adult. Any help would be appreciated.
>
> You can view the photos of the bird here on these 3 checklists:
>
> https://ebird.org/checklist/S251486607 >
> https://ebird.org/checklist/S251577330 >
> https://ebird.org/checklist/S251215877 >
> -----------------------
> Rachel Kolokoff Hopper
> Ft. Collins, CO
>
>
> Archives: https://listserv.ksu.edu/birdwg01.html
Date: 6/20/25 12:53 am From: Davy Bosman <bosman.davy...> Subject: Re: [BIRDWG01] Colorado Booby ID
Hi,
Maybe somebody should go back to that tree. See if there is some dry
'droppings' to be collected with a wet (not saliva) eartip? Or maybe the
bird shed a plume? If that is not already done of course. There must be a
genotypical difference, because why otherwise is this a seperate species?
Grtz. D.
Op do 19 jun 2025, 23:17 schreef David Sibley <sibleyguides...>:
> Following up on this after more photo study. I still think this bird is a
> better match for Atlantic Brown Booby, but can't rule out Cocos with
> certainty.
>
> For comparison, this subadult Brown from Maryland is an almost exact match
> - https://macaulaylibrary.org/asset/624857879 > This Cocos from Costa Rica is also very close -
> https://macaulaylibrary.org/asset/629034516 >
> Bill color, bill shape, and eye color seem to be no help in ID.
>
> One thing that does seem fairly consistent in photos I've looked at is
> that Cocos has a wider ring of bare skin behind the eye, and by that
> feature the Colorado bird matches Brown.
>
> And the bare skin on the chin of Cocos seems to average a little drabber
> and greener, Brown Booby more yellow, again the CO bird matches Brown.
>
> Those are pretty much the only differences I can see for a subadult female
> like this, and for now I would not feel confident identifying either
> species out of range based on those things. But maybe one could argue that
> Colorado is within the "expected" range for Brown Booby?
>
> Colorado's prior record looks like an adult female Atlantic Brown Booby.
> Cocos adult female typically has a greener face and darker brownish bill
> (but there is overlap).
>
> Best,
> David
>
> <sibleyguides...>
> www.sibleyguides.com
>
>
>
> > On Jun 18, 2025, at 11:57 AM, Rachel Hopper <hopkohome8...>
> wrote:
> >
> > Colorado just had its second record of a booby, found on June 16th &
> seen early again on the 17th after which it disappeared.
> >
> > It was found in a tree out on the prairie in far SE CO. No water body
> even close.
> >
> > There are several photos of the bird, which did take flight a few times,
> always coming back to land in an Elm tree. At one point it was on the
> ground.
> >
> > We are trying to determine if this is a Brown Booby or Cocos Booby.
> Possibly not a full adult. Any help would be appreciated.
> >
> > You can view the photos of the bird here on these 3 checklists:
> >
> > https://ebird.org/checklist/S251486607 > >
> > https://ebird.org/checklist/S251577330 > >
> > https://ebird.org/checklist/S251215877 > >
> > -----------------------
> > Rachel Kolokoff Hopper
> > Ft. Collins, CO
> >
> >
> > Archives: https://listserv.ksu.edu/birdwg01.html >
>
> Archives: https://listserv.ksu.edu/birdwg01.html >
Date: 6/19/25 6:29 pm From: Wayne Hoffman <whoffman...> Subject: Re: [BIRDWG01] Colorado Booby ID
Hi -
Your mention that both this bird and the previous Colorado bird were females reminded me that when "Brown" Boobies (later split as Cocos Boobies) became regular in small numbers on the Oregon coast a decade or so ago, both adults and subadults were occurring, but no birds identifiable as adult male Cocos Boobies had been documented, at least as of 2018 when I left Oregon. So I wonder if female "Brown" Boobies are more likely to wander than males? Similar sex biases in vagrancy are documented in other birds (e.g. Ancient Murrelets).
Wayne Hoffman
----- Original Message -----
From: "David Sibley" <sibleyguides...>
To: "BIRDWG01" <BIRDWG01...>
Sent: Thursday, June 19, 2025 5:17:22 PM
Subject: Re: [BIRDWG01] Colorado Booby ID
Following up on this after more photo study. I still think this bird is a better match for Atlantic Brown Booby, but can't rule out Cocos with certainty.
Bill color, bill shape, and eye color seem to be no help in ID.
One thing that does seem fairly consistent in photos I've looked at is that Cocos has a wider ring of bare skin behind the eye, and by that feature the Colorado bird matches Brown.
And the bare skin on the chin of Cocos seems to average a little drabber and greener, Brown Booby more yellow, again the CO bird matches Brown.
Those are pretty much the only differences I can see for a subadult female like this, and for now I would not feel confident identifying either species out of range based on those things. But maybe one could argue that Colorado is within the "expected" range for Brown Booby?
Colorado's prior record looks like an adult female Atlantic Brown Booby. Cocos adult female typically has a greener face and darker brownish bill (but there is overlap).
Best,
David
<sibleyguides...>
www.sibleyguides.com
> On Jun 18, 2025, at 11:57 AM, Rachel Hopper <hopkohome8...> wrote:
>
> Colorado just had its second record of a booby, found on June 16th & seen early again on the 17th after which it disappeared.
>
> It was found in a tree out on the prairie in far SE CO. No water body even close.
>
> There are several photos of the bird, which did take flight a few times, always coming back to land in an Elm tree. At one point it was on the ground.
>
> We are trying to determine if this is a Brown Booby or Cocos Booby. Possibly not a full adult. Any help would be appreciated.
>
> You can view the photos of the bird here on these 3 checklists:
>
> https://ebird.org/checklist/S251486607 >
> https://ebird.org/checklist/S251577330 >
> https://ebird.org/checklist/S251215877 >
> -----------------------
> Rachel Kolokoff Hopper
> Ft. Collins, CO
>
>
> Archives: https://listserv.ksu.edu/birdwg01.html
Date: 6/19/25 2:18 pm From: David Sibley <sibleyguides...> Subject: Re: [BIRDWG01] Colorado Booby ID
Following up on this after more photo study. I still think this bird is a better match for Atlantic Brown Booby, but can't rule out Cocos with certainty.
Bill color, bill shape, and eye color seem to be no help in ID.
One thing that does seem fairly consistent in photos I've looked at is that Cocos has a wider ring of bare skin behind the eye, and by that feature the Colorado bird matches Brown.
And the bare skin on the chin of Cocos seems to average a little drabber and greener, Brown Booby more yellow, again the CO bird matches Brown.
Those are pretty much the only differences I can see for a subadult female like this, and for now I would not feel confident identifying either species out of range based on those things. But maybe one could argue that Colorado is within the "expected" range for Brown Booby?
Colorado's prior record looks like an adult female Atlantic Brown Booby. Cocos adult female typically has a greener face and darker brownish bill (but there is overlap).
Best,
David
<sibleyguides...>
www.sibleyguides.com
> On Jun 18, 2025, at 11:57 AM, Rachel Hopper <hopkohome8...> wrote:
>
> Colorado just had its second record of a booby, found on June 16th & seen early again on the 17th after which it disappeared.
>
> It was found in a tree out on the prairie in far SE CO. No water body even close.
>
> There are several photos of the bird, which did take flight a few times, always coming back to land in an Elm tree. At one point it was on the ground.
>
> We are trying to determine if this is a Brown Booby or Cocos Booby. Possibly not a full adult. Any help would be appreciated.
>
> You can view the photos of the bird here on these 3 checklists:
>
> https://ebird.org/checklist/S251486607 >
> https://ebird.org/checklist/S251577330 >
> https://ebird.org/checklist/S251215877 >
> -----------------------
> Rachel Kolokoff Hopper
> Ft. Collins, CO
>
>
> Archives: https://listserv.ksu.edu/birdwg01.html
I believe this bird is a late juv Brown Booby, possibly of the Atlantic form based on bill shape. The underwing pattern would suggest Cocos if this were an adult, but juvs of both species show a similar underwing. The clincher is the eye color. Cocos Boobies have dark eyes, Browns have pale eyes. Great photos for making an ID. -Doug Pratt
> On Jun 18, 2025, at 11:57 AM, Rachel Hopper <hopkohome8...> wrote:
>
> Colorado just had its second record of a booby, found on June 16th & seen early again on the 17th after which it disappeared.
>
> It was found in a tree out on the prairie in far SE CO. No water body even close.
>
> There are several photos of the bird, which did take flight a few times, always coming back to land in an Elm tree. At one point it was on the ground.
>
> We are trying to determine if this is a Brown Booby or Cocos Booby. Possibly not a full adult. Any help would be appreciated.
>
> You can view the photos of the bird here on these 3 checklists:
>
> https://ebird.org/checklist/S251486607 >
> https://ebird.org/checklist/S251577330 >
> https://ebird.org/checklist/S251215877 >
> -----------------------
> Rachel Kolokoff Hopper
> Ft. Collins, CO
>
>
> Archives: https://listserv.ksu.edu/birdwg01.html
"Some people have been kind enough to call me a fine artist. I've always called myself an illustrator. I'm not sure what the difference is." - Norman Rockwell
H. Douglas Pratt, Ph. D.
Ornithologist, illustrator, musician
1205 Selwyn Lane
Cary, NC 27511
Emeritus Curator of Birds
North Carolina Museum of Natural Sciences
11 West Jones Street
Raleigh NC 27601
Date: 6/18/25 2:44 pm From: Peter Pyle <ppyle...> Subject: Re: [BIRDWG01] Booby ID
I agree with Wayne on Cocos being more likely in southeastern Colorado. I had already forwarded the links to Eric and here is his response:
"Just realized i didn’t look at the checklist with the better pictures. After looking at them i agree that it looks like a female Cocos based primarily on the bill color, mostly pink, and also on the concave shape of the culmen . Although it is subadult there is enough of the bill color to make an identification. The iris is intermediate in darkness, but that is more variable in females." Cheers, Peter On 6/18/2025 2:32 PM, Wayne Hoffman wrote: > Hi - > > I do not contest your suggestion the features you describe tend to favor Brown Booby, but I am not sure that "the location strongly favors Brown." Many years ago I chased a Blue-footed Booby in central Texas, and I doubt it got there via the gulf. In addition, I think there is a pattern of at least occasional vagrancy of seabirds from the Sea of Cortez into the southwest. Oklahoma has a Great Frigatebird record, Blue-footed Booby vagrancy has reached Arizona, Nevada, Utah, and New Mexico, as well as Texas. > > Wayne Hoffman > > ----- Original Message ----- > From: "David Sibley" <sibleyguides...> > To: "BIRDWG01" <BIRDWG01...> > Sent: Wednesday, June 18, 2025 3:59:23 PM > Subject: Re: [BIRDWG01] Booby ID > > I did a lot of work on this question a year ago, starting from the excellent work by Eric VanderWerf and looking at lots of photos. This bird is a subadult, and I could not find any reliable way of separating Brown and Cocos Booby at that age. The yellow facial skin and pinkish bill seem more typical of Atlantic (but can be matched by some Cocos), and the impression that the neck is darker than the back favors Atlantic. Other features like forehead color and underwing pattern can be helpful on adults but not on subadults. > > As Paul says the location strongly favors Brown. All of the identifiable photos (adults) that I saw from eastern North America are Brown, but there is one Cocos record from the Caribbean off Panama. > > Best, > David > > <sibleyguides...> > www.sibleyguides.com > > > >> On Jun 18, 2025, at 2:25 PM, Paul Lehman <00000ae015dd4920-dmarc-request...> wrote: >> >> Slide presentation from wfo meeting in San Diego last October. Bill color potential differences would suggest Colorado bird may be a Cocos, given all the brownish in the bill, which seems surprising in Southeast Colorado where one would think it's a bird up from the Gulf of Mexico and therefore a Brown. >> Paul Lehman >> Sent from AOL on Android >> >> Archives: https://listserv.ksu.edu/birdwg01.html > > Archives: https://listserv.ksu.edu/birdwg01.html > > Archives: https://listserv.ksu.edu/birdwg01.html
Date: 6/18/25 2:32 pm From: Wayne Hoffman <whoffman...> Subject: Re: [BIRDWG01] Booby ID
Hi -
I do not contest your suggestion the features you describe tend to favor Brown Booby, but I am not sure that "the location strongly favors Brown." Many years ago I chased a Blue-footed Booby in central Texas, and I doubt it got there via the gulf. In addition, I think there is a pattern of at least occasional vagrancy of seabirds from the Sea of Cortez into the southwest. Oklahoma has a Great Frigatebird record, Blue-footed Booby vagrancy has reached Arizona, Nevada, Utah, and New Mexico, as well as Texas.
Wayne Hoffman
----- Original Message -----
From: "David Sibley" <sibleyguides...>
To: "BIRDWG01" <BIRDWG01...>
Sent: Wednesday, June 18, 2025 3:59:23 PM
Subject: Re: [BIRDWG01] Booby ID
I did a lot of work on this question a year ago, starting from the excellent work by Eric VanderWerf and looking at lots of photos. This bird is a subadult, and I could not find any reliable way of separating Brown and Cocos Booby at that age. The yellow facial skin and pinkish bill seem more typical of Atlantic (but can be matched by some Cocos), and the impression that the neck is darker than the back favors Atlantic. Other features like forehead color and underwing pattern can be helpful on adults but not on subadults.
As Paul says the location strongly favors Brown. All of the identifiable photos (adults) that I saw from eastern North America are Brown, but there is one Cocos record from the Caribbean off Panama.
Best,
David
<sibleyguides...>
www.sibleyguides.com
> On Jun 18, 2025, at 2:25 PM, Paul Lehman <00000ae015dd4920-dmarc-request...> wrote:
>
> Slide presentation from wfo meeting in San Diego last October. Bill color potential differences would suggest Colorado bird may be a Cocos, given all the brownish in the bill, which seems surprising in Southeast Colorado where one would think it's a bird up from the Gulf of Mexico and therefore a Brown.
> Paul Lehman
> Sent from AOL on Android
>
> Archives: https://listserv.ksu.edu/birdwg01.html
Date: 6/18/25 2:16 pm From: Joseph Morlan <jmorlan...> Subject: Re: [BIRDWG01] Booby ID
I corresponded with Eric about this problem and he suggested that Cocos has a more curved bill, more tapered than Brown which has a straight culmen. This apparently works with immatures as well as adults. Another possible clue is eye color which is pale on Brown and dark on Cocos. This works with adults, but Eric said that it may be helpful on immatures as well, but more data is needed.
Bill looks curved and tapered to me. Eye is mostly dark but somewhat ambiguous.
I'll forward this to Eric to see if he has an opinion.
On Wed, 18 Jun 2025 15:59:23 -0400, David Sibley <sibleyguides...> wrote:
>I did a lot of work on this question a year ago, starting from the excellent work by Eric VanderWerf and looking at lots of photos. This bird is a subadult, and I could not find any reliable way of separating Brown and Cocos Booby at that age. The yellow facial skin and pinkish bill seem more typical of Atlantic (but can be matched by some Cocos), and the impression that the neck is darker than the back favors Atlantic. Other features like forehead color and underwing pattern can be helpful on adults but not on subadults. > >As Paul says the location strongly favors Brown. All of the identifiable photos (adults) that I saw from eastern North America are Brown, but there is one Cocos record from the Caribbean off Panama. > >Best, >David > ><sibleyguides...> >www.sibleyguides.com > > > >> On Jun 18, 2025, at 2:25?PM, Paul Lehman <00000ae015dd4920-dmarc-request...> wrote: >> >> Slide presentation from wfo meeting in San Diego last October. Bill color potential differences would suggest Colorado bird may be a Cocos, given all the brownish in the bill, which seems surprising in Southeast Colorado where one would think it's a bird up from the Gulf of Mexico and therefore a Brown. >> Paul Lehman >> Sent from AOL on Android >> >> Archives: https://listserv.ksu.edu/birdwg01.html > > >Archives: https://listserv.ksu.edu/birdwg01.html -- Joseph Morlan, Pacifica, CA
Date: 6/18/25 1:00 pm From: David Sibley <sibleyguides...> Subject: Re: [BIRDWG01] Booby ID
I did a lot of work on this question a year ago, starting from the excellent work by Eric VanderWerf and looking at lots of photos. This bird is a subadult, and I could not find any reliable way of separating Brown and Cocos Booby at that age. The yellow facial skin and pinkish bill seem more typical of Atlantic (but can be matched by some Cocos), and the impression that the neck is darker than the back favors Atlantic. Other features like forehead color and underwing pattern can be helpful on adults but not on subadults.
As Paul says the location strongly favors Brown. All of the identifiable photos (adults) that I saw from eastern North America are Brown, but there is one Cocos record from the Caribbean off Panama.
Best,
David
<sibleyguides...>
www.sibleyguides.com
> On Jun 18, 2025, at 2:25 PM, Paul Lehman <00000ae015dd4920-dmarc-request...> wrote:
>
> Slide presentation from wfo meeting in San Diego last October. Bill color potential differences would suggest Colorado bird may be a Cocos, given all the brownish in the bill, which seems surprising in Southeast Colorado where one would think it's a bird up from the Gulf of Mexico and therefore a Brown.
> Paul Lehman
> Sent from AOL on Android
>
> Archives: https://listserv.ksu.edu/birdwg01.html
Date: 6/18/25 11:26 am From: Paul Lehman <00000ae015dd4920-dmarc-request...> Subject: [BIRDWG01] Booby ID
Slide presentation from wfo meeting in San Diego last October. Bill color potential differences would suggest Colorado bird may be a Cocos, given all the brownish in the bill, which seems surprising in Southeast Colorado where one would think it's a bird up from the Gulf of Mexico and therefore a Brown.
Paul Lehman
Sent from AOL on Android
A friend found this warbler in SE Colorado in late May of this year. He is thinking Yellow-rumped X Cape May but is interested in other thoughts on what hybrid it might be. You can see the bird here: https://www.rkhphotography.net/Hybrid-Warbler -----------------------
Rachel Kolokoff Hopper
